Frequency divider



14, 1951 G. K. JENSEN FREQUENCY DIVIDER 5 Shecs-Sheet 2 Filed Dec. 1, 1949 ATTORN EY Aug. 14, 1951 G. K. JENSEN FREQUENCY DIVIDER 5 Sheets-Sheet 3 Filed Dec. 1, 1949 mm E 3124 PDnEbO q A mTI 1H. v w J JENSEN K W n n m M R m 0;. M r N61 0 OF n\ 0P l 29m mac :05

$56 ommN z mm W51 Emma 55;

E535 526 $263 2 OF 3336 55mm IUH ATTORNEY G. K. JENSEN FREQUENCY DIVIDER Filed Dec. 1, 1949 I w l Sa :1: T 0F mp 1 u \L J h 8 2: m 0F mzolomm wzawmoonw vmL h 0F 53:2 o m n Q P mm r II III IIIL llllllllllllllll |l 3mm GAROLD K. JENSEN ATTOR N EY Patented Aug. 14, 1951 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757).

6 Claims.

This invention relates to electric frequency divider systems in general and in particular to a divider system capable of receiving a signal of a selected frequency to produce an output signal at a selectable sub-multiple of the input signal.

In numerous applications of electric equipment it is desirable to obtain frequency division so that an input signal at a frequency which may be either fixed or variable may provide an output signal at a selected sub-multiple thereof. To obtain operation of this nature at a constant, selected division ratio it is not a simple matter to employ resonant electric circuits. On the other hand where input signals may be rather high in frequency, typically one megacycle per second, resonant electric circuits are generally used. It is immediately apparent therefore that ordinary previously available combinations of circuits would not be suited to provide constant ratio frequency division over a wide range of input frequencies. For convenience of operation or selection of the frequency division ratio at which operation is to be maintained it has been advantageous to employ counter circuits operating in a decimal digit system controlled by decimal digit selectors, manually operated, one for each decimal digit of the division ratio. With such decimal digit selectors each digit of the division ratio may be independently and rapidly inserted. Such decimal digit selection is known to all familiar with electrical measurements because it is just this sort of operation that is employed with resistance decade boxes in electrical bridge measurements where the units, tens, hundreds, and so forth decimal digit values of resistance may be inserted separately as by a multiple position switch for each digit.

It is accordingly an object of the present invention to provide frequency division apparatus which will operate over a wide frequency range to provide output signals at a frequency lower than the input frequency.

'Another object of the present invention is to provide frequency division apparatus which will deliver output signals of a frequency which is a selectedsub-multiple of the frequency of input signals.

Other and further objects and features of the present invention will become apparent upon a careful consideration of the following detailed description when taken in conjunction with the accompanying drawings in which:

Fig. 1 shows partly in block form apparatus constructed in accordance with the teachings of the present invention;

Fig. 2 is a schematic diagram of a multi-stage scale-of-two counter circuit as employed in the apparatus of "the present invention showing input; output; and reset connections thereto, and

Figs. 3, 4 and 5 are schematic diagrams showing additional components of the block diagram of Fig. 1.

In accordance with the basic features of the present invention, frequency division by any selected whole number is obtained with a plurality of digit dividers, one for each decimal digit of the division ratio. As many digit dividers are ordinarily employed as the maximum number of digits desired in the division ratio, typically four where division ratios up to 9999 to 1 are desired. The digit dividers are connected for operation in sequence, that is, a first divider allotted typically to the units digit of the division ratio receives input signals and supplies output signals to the second divider (tens). In turn the tens divider supplies signals to the hundreds divider, the hundreds divider to the thousands divider and so on if more digits are employed. All dividers except the last initially count up to the value of the corresponding digit of the division ratio, then reset themselves to subsequently provide output signals to the succeeding divider for each succeeding tenth-input signal to the particular divider. The last divider provides an output whenever the desired value of the last digit is reached, at which time it also provides a reset signal to return all of the dividers to a reference condition from which to repeat operation.

With reference now to Fig. 1 Of the drawing, a frequency divider circuit is shown therein principally in block form. Terminal 38 in the upper left hand corner receives the input signals. These signals may be of a pulse nature or a sinusoidal nature as typical illustrations. For the latter type of input signals it is desirable to obtain short duration pulse type signals to which end the clipper-shaper 39 is employed. The output from this clipper-shaper 39 is applied to the terminal I4 of a group of binary dividers 40 which are typically constructed in accordance with the circuit shown in Fig. 2, having several stages of scale-of-two counter circuits which will exist in various combinations of conductivity conditions for various input signals. Selector switches in block 4!, of Fig. 1, are connected to the divider 4G to provide output signals for selected combinations of binary divider conditions. For example, if the units digit of the division ratio corresponds to the numeral 8 then the selector switches 4| are set, as hereinafter described, to produce an output signal at the end of a count of 8. When this selected combination of binary divider conditions is attained, the variable mixer #32 supplies a keying signal to the trigger circuit 43 to produce an output pulse signal. Trigger circuit 43 is preferably of the Eccles-Jordan type possessing two conditions of stability and having two separate input signal dividers 49through trigger circuit 6|.

. 3 paths. In an initial condition of stability, trigger circuit 43 is responsive to signals from variable mixer 42 which signals can initiate the second condition of stability theren. In this con dition subsequent signals from variable mixer 32 are ineffective until the first condition of stability is again obtained responsive to a reset signal obtained from the output amplifier 60 as later ex-' plained.

Upon triggering of the circuit 33 by a signal from the variable mixer 42, a pulse type signal is supplied to the reset circuits 46 to reset the binary dividers 40 to the reference condition.

In addition to the previously described connections to the binary divider circuit d through selector switches 4|, additional fixed position output connections are made to anodes of the binary dividers in a. combination indicative of the count of ten. These fixed connections supply signals to fixed mixer 47 which may be similar to the variable mixer 42. In this manner after the trigger circuit 23 is operated by variable mixer i2 resetting binary dividers 4!] to the reference condition, variable mixer 42 is in operative and binary dividers 40 will continue to register input signals until the count of ten is registered. Upon each registry of this count of ten, fixed mixer Ll? becomes operative to trigger the one-shot multivibrator 4B which as its name implies, possesses one single stable state together with an unstable state which may persist for a short period of time. The output signal from this one-shot multivibrator a8 is also supplied to the reset circuits 26 to provide reset of the binary dividers it to an initial or reference combination of conductivity states. In this manner after the initial count corresponding to the units value of the divisionv ratio is registered by the binary dividers 46, trigger circuit 43 is inoperative and one signal is obtained at the one-shot multivibrator is for each ten succeeding input signals.

The output from one-shot multivibrator 38 is supplied to the binary dividers 40 of a succeeding decade circuit for the tens digit of division. These circuits are identical to those previously described for the units digit section, however the signals as obtained from the one-shot multivibrator 48 are of a pulse nature so that a clippershaper such as 3% is not normally required. The

value of the tens decimal digit is registered by the binary dividers 49 to produce conduction by the variable mixer 50 with subsequent reset of binary After this reset the tens dividers also count in multiples of ten through operation of the fixed mixer M with reset circuits as before and provides signals to the hundreds digit section.

Th apparatus for the hundreds digit may be identical in design and operation to that of the tens digit, first countin off the selected value of the hundreds digit then counting in multiples of ten providin output pulses from the one-shot multivibrator 53 which are supplied to the thousands binary divider 54.

Where the division ratio does not normally exceed 10,000 or even an extreme of approximately 25,000 only four digit circuits are required-for such an apparatus th thousands digit circuit would be the last. The last or thousands digit circuits are somewhat different from those for the previous digits since there is no longer the necessity for counting'in multiples of ten after the value of the thousands digit is registered. For this reason the fixed mixer such as 41 and the one-shot multivibrator such as 48 of the units digit section are not present in the circuit for the thousands digit. Instead, output signals from the variable mixer 55 which again may be similar in construction to the variable mixer 42, are supplied through a multiple position switch 56 to a one- .shot multivibrator 51.

vibrator are sup-plied first to reset circuits 58 to provide reset of the thousands binary dividers 54 to reference conditions. Additionally output signals from one-shot multivibrator 51 are suppliedto amplifier 60 from which they are obtained as output frequency divided pulse type signals. Each signal from amplifier is also delivered to each of the bi-stable triggering circuits :33, BI and 62 to return them to the condition wherein they are responsive to signals from the corresponding variable mixers 42, 50 and 63. At this point and by the action of trigger circuits 43, 6| and 62' all binary dividers and trigger circuits are again in the initial reference condition from which another complete cycle of operation as thus described may commence.

The type of operation thus described will take place whenever there is a value other than zero set in each of the division ratio selectors. To provide operation for the division ratios wherein zero might appear in one of the digit positions, additional circuitry is involved. In the first place the multiple position switches 64, 65, 66 and 56 compensate for the presence of a zero in any of the tens, hundreds and thousands digit selectors. The switches 6Q, 65, 66 and 56 are ganged with corresponding decimal digit selector switches that is, switch 64 is ganged for operation through ten positions with the selector switches ll, switch 65 ganged for operation with the selector switches BI and so on. When switch 64 is in any position other than zero position itsupplies a signal from trigger circuit 53 and associated amplifier 33A to terminal 68 at the #1 position of switch 65 each time the value of the units digit is registered by binary dividers 40 at the start of a division cycle. If switch 65 is in the zero position when such signal is received, that signal is delivered to terminal of switch 66. Again if switch is in the zero position the same signal is delivered to amplifier 70. If also switch 56 is in the zero position, signals from amplifier 10 appearin at terminal H will be delivered to the one-shot multivibrator 5! to cause operation thereof to provide an output signal from amplifier E50. This operation is experienced whenever the division ratio nine to one or less. Where a zero in the divi sion ratio is for a lower order digit such as the units digit, the selector switches 4!, as later described, will prevent operation of the variable mixer 12. However the fixed mixer '41 will still operate providing an output signal for each ten input signals. It is these signals that are delivered for counting by the succeeding decade stage as originally described.

Details of the components shown in block form in Fig. l are shown in additional figures and will now be discussed. With reference first to Fig. 2, details are shown therein of a typical multi-stage scale-of-two counter as employed in the binary dividers G0 etc. for each digit of the frequency division ratio. The fundamental features of this multi-stage scale-of-two counter circuit are probably familiar, each stage being of the Eccles-Jordan type having two tubes ,receiving an input signal at a first frequency/and providing an output signal at half that frequency. To provide a possible ten positions, or combinations of counter stages, four scale-of-two counter circuits connected in cascade are employed. It should be borne in mind that on all of Figs. 2, 3, 4 and 5, dotted-in portions are shown to indicate generally the portions of each schematic drawing corresponding to the blocks of Fig. 1.

The apparatus of Fig. 2 is shown as having triode type electron tubes |0-A, Ill-B, lI-A, Il-B, l2A, l2--B, l3-A and l3-B. These tubes are cross-connected in pairs in which only one tube of each pair can be conductive at any instant. Typically pulse type input signals are applied at input terminal l4. These signals are delivered through uni-lateral impedance coupling elements such as the crystal diodes l5, I6, I! and I8 to the grids of tubes l0A and |0B in parallel. As polarized, the uni-lateral impedance elements are set to deliver only negative pulses to the tube grids to produce current cut off of the conductive tube of the pair thereby initiating trigger action. Thus the circuit of tubes llJ-A and l0-B will operate from one conductivity condition to another undergoing a complete cycle of operation in response to two successive input pulses at terminal M.

The anode of tube l0B is connected through uni-lateral impedance elements I9, 20, 2| and 22 which may also be of the crystal diode type to the grids of tubes ll-A and H-B in parallel which are connected in a second trigger circuit similar to the first. Responsive to each initiation of current flow in tube l0B, the negative voltage surge at the anode thereof produces cut off of the conductive tube I l-A or i lB. Since each second input pulse at terminal I4 will provide this condition of tube IU-B, two complete cycles of operation of the circuit of tubes Ill-A and Ill-B (4 input pulses) are required to produce a cycle of operation of the circuit of tubes ll-A and H-B.

In a similar manner a third trigger circuit of tubes I2A and l2-B is connected to the anode of tube l IB and experiences a complete cycle of operation for each two cycles of operation of circuit HA and ll-B. Likewise a fourth circuit of tubes l3-A and l3-B is connected to the anode of tube l2-B for half frequency operation therefrom.

An initial reference state for the trigger circuits may be selected in which all of the right hand tubes are conductive (Ill-B, il-B, l2-B, I3B). In this zero condition all of the left hand anodes are near (B+) potential. After a first input pulse to terminal [4, tube Ill-A will be conductive and the plate of tube ill-B near (3+) potential. These conditions as well as those brought about in this and other trigger circuits upon application of nine additional input pulses are tabulated below.

Condition of Plates nonconductive, conductive) Count l0-A 1043 11-2. 'llBll2-AI12-B l3-A 13-B i i i t. i r- The selector switches shown in block in Fig. 1, corresponding to block 4| etc. are represented in Fig. 2 as switches 3|, 32 and 33.

For determining the state of the stages of the counter to produce output signals when selected states are reached, a form of coincidence or gate circuit is used such as the variable mixers 42 etc. A typical circuit of this nature is shown in part of Fig. 3 and includes primarily the two electron tubes 23 and 24. Tube 24 is a triple grid tube and receives at the three grids 25, 26 and 21 signals from the trigger circuit selector switches 3|, 32, 33 of Fig. 2. All grids 25, 26 and 21 are normally quite heavily biased with respect to the cathode because of the plus-55 volts at the cathode. However when these grids are simultaneously brought to high potential as a result of their connection through switches 3|, 32 and 33 to non-conductive anodes of the trigger circuits of Fig. 2, the anode current path of tube 24 can be rendered conductive. To raise the potential of screen grid 25, considerable current must be supplied thereto. This current is provided by the operation of the amplifier tube 23 whose anode is coupled to grid 26 through capacitance 28. Resistance 29 provides a return current path for capacitance 28 and uni-lateral impedance element 33 clamps the grid 26 to suppress negative excursions thereof.

Application of signals from the typical counter tubes of Fig. 2 to the grids or gating circuits as shown in Fig. 3 is accomplished through the three section multiple position switches indicated in Fig. 2 by numerals 3|, 32 and 33. These switches are ganged together and may be operated manually with rotation in synchronism for each decimal digit unit. The grid of tube 23 (Fig. 3) is connected to the movable contact of switch 3|, (terminal B), grid 2? of tube 24 (Fig, 3) is connected to the movable contact of switch 32 (terminal D) while grid 25 of tube 24 (Fig. 3) is connected to the movable contact of switch 33 (terminal E). In accordance with the tabulation previously given for the various oounts," corresponding stationary contacts for the switches 3|, 32, 33 are connected to appropriat anodes of the counter tubes, connections being made to tubes having positive designation. Connections of the stationary contacts for the zero position of switches 31, 32, 33 is not required.

The stationary contacts of switch 3| are connected in the anode circuits of tubes tit-A and Ill-13, the stationary contacts of switch 32 in the anode circuits of tubes ii-A and ilB, and the stationary contacts of switch 33 in the anode circuits of tubes 2--A, E2-B and l3B.

As an illustration of this method of connection, upon inspection of the previous tabulation it is seen that for a typical count of l. with switches 3|, 32, 33 (Fig. 2) in the 1 position, the anodes of tubes Iii-B, HA, lQ-A, and S-A. are at the high potential whereas the opposing anodes are at the low potential. Connection of the high potential anodes having the positive indication enclosed in parenthesis to the stationary contacts of the switches ill, 32, 33 controlling the three gating input circuits may thus be made. With this circuit arrangement each time the typical count of 1 is reached tube 23 will be rendered conductive.

At this point it is well to note that the signal inversion introduced by tube 23 must be taken into consideration. Hence the connection of the grid of tube 23 is made to the opposite anode from that 'given by the plus sign in the tabulation 7 tube lll-A). Further, if desired, the voltage amplification produced by tube 23 may in part be counter-balanced by the connection to only a part of the total anode circuit load resistance as shown in Fig. 2. For the other trigger circuits, connection is made direct to the anode terminals.

Coupling condensers 3:3 and 35 Fig. 2, bypassed by resistances 36 and 31 are employed in the signal path from switches 32 and 33 to grids 2? and 25. This connection assists in the maintenance of low D.-C. potential at the grids 25 and 27 yet supplies the full signal amplitude to the grids upon occurrence of the trigger operation in .a trigger circuit such as ll-A, H--B.

The previously mentioned trigger circuit 23 is shown in Fig. 3 having the tubes 34 and 45 together with a keying tube :'l5A. This circuit receives set signals from the anode of variable mixer tube 24 which bring tube 44. to conduction each time it is non-conductive upon initiation of conduction by tube 24. Tube lE-A receives master reset pulses from amplifier of Fig. each time a quantity of input signals equal to the value of the division ratio is counted by the overall system. By these signals, tube .5-A is brought to momentary conduction to bring the trigger circuit tube 45 to conduction.

Additional components of the overall apparatus which have not been previously described will now be described in considerable detail. A first component to be described appears in Fig. 3 and is identified therein as the reset circuits of block 56. As shown these reset circuits include four biased electron tubes l2, l3, l4 and 75 which are normally nonconductive. Positive polarity input signals are applied to these tubes in parallel from the anode of tube 45 and from the one-shot multivibrator anode 82 of Fig. 4. The anodes of tubes 12, 73, M and F5 are connected individually to the right hand anodes of the tubes of the corresponding trigger circuits as typified in Fig. 2 and indicated thereon. With these connections each time a positive pulse is applied to reset grid terminal it, conduction by the reset tubes through the corresponding anode load resistance of the trigger circuits of Fig. 2 will cause the trigger circuits to achieve a zero condition in which the right hand tube of each circuit is conductive.

Details of the fixed mixers such as All and the one-shot multivibrator such as 48 for the units, tens and hundreds digits are shown in Fig. 4. The fixed mixer 47 includes the electron tubes Ti and 18 in circuit construction practically identical to that of the previously discussed tubes 23 and 24 in the variable mixer 42 (Fig. 3) differing therefrom only in the source of input signals. As indicated by the lettered terminals referring to Fig. 2, the grid of tube 11 receives signals from the anode of tube IUB, grid it receives signals from the anode of tube l iB and grid 89 receives signals from the anode of tube l3-B. An in spection of the previous tabulation will show that this connection corresponds to the conditions for the count of wherein these anodes possess posi tive notation and is the first time in the sequential tabulation that such a condition appears. From this circuit arrangement therefore it is seen that tube l8 will achieve conduction each time the binary divider cooperative therewith achieves the ten count combination. I

The one-shot multivibrator 48 is shown in Fig. 4 as those components associated with the electron tubes BI and 82. By virtue of the capacitance 84 coupling the anode of tube BI and the grid of tube '82 the normal condition for the oneshot multivibrator is that wherein tube 82 is conductive. This condition altered however upon the initiation of conduction in tube is with the resulting drop in potential across resistance 83. Tube Si is thus brought to conduction for a period of time determined primarily by the time constants of the circuits associated with capacitance 84. In this manner then, a short duration positive pulse is produced at the anode of tube 82 while a short duration negative pulse is produced at the anode of tube 8!. The positive pulse from the anode of tube 82 is delivered to the reset circuits 45 (Fig. 3) in a path parallel with the. reset signal from trigger circuit 43. The negative signal from the anode of tube 8i goes to the succeed ing binary divider 45 (Fig. l) in the tens digit circuit as input pulses thereto.

The thousands or last decade circuit as previe ously mentioned is different from the circuit for the other digits in that the fixed mixer such as ll or 51 is not employed. Additional diiierences will be noted in Fig. 5 which shows circuit details of the variable mixer 55, the one-shot multivi brator 5i, amplifiers S9 and switches and 59 and reset circuits 5%. The binary divider circuit 54 for the thousands section is as shown in Fig. 2 except it does not contain the fixed output paths indicated by A, C and F. Only the variable signal paths B, D and E are employed delivering signals as indicated on Fig. 5 to grids 85, and 8? respectively of electron tubes 38 and 33. The circuit of these tubes 88 and 89 is again similar to the first discussed circuit of tubes 23 and 24 in Fig. 3. A difference lies however in that the output of tube 8% is connected through switch 56 to the one-shot multivibrator of tubes 9d and 9!. This one-shot multivibrator may be similar in structure to the previously described multivibrator is of Fig. 4. The negative pulse output as obtained at the anode of tube 951 responsive to conduction by tube 89 is supplied direct to the amplifier tube Q2 which is the primary component of amplifier 6i) in Fig. 1. To provide output signals from the system when the thousands decade selector is in zero position the direct signal path from the hundreds decade output circuit through the zero position of switch 52; to amplifier tube 52 is included. 7

Reset signals for the thousands binary dividers 54 (Fig. 1) are obtained from the reset tubes 93, 94, 55 and 96 of Fig. 5 and are delivered in the same manner as previously described to the right hand anodes of the binary divider circuits. These reset signals are derived from the short duration positive pulse signals from the anode of tube 9|. When the thousands decade selector is in the zero position,the' one-shot multivibrator 51 of tubes 90 and 9! is connected through the zero position of switch 56 and the amplifier tube 91 for operation to produce output signals responsive to zero bypassed signals from the hundreds section (switch 56 in Fig. 1)

With the overall circuit and its components thus described, the true import of the present invention may be readily visualized.

Although certain specific embodiments of this invention have been disclosed and described it is to be understood that they are merely illustrative of this invention and modifications may, of course, be made without departing from the spirit and scope of the invention as defined in thelappe nded claims.

The invention described herein may be manufactured and. used by or for the Government of the United States of America for governmental purposes Without the payment of any royalties thereon or therefor.

What is claimed is:

1. A frequency divider operative to produce division of an applied signal by selectable whole number ratios comprising, a plurality of divider sections connected in cascade, one for each decimal digit of the division ratio, counter means within each section counting first a number of signals equal to the value of the corresponding decimal digit then providing a signal to a sueoeeding section for each tenth input pulse thereto, an output signal path providing an output signal each time the value of the highest order decimal digit of the division ratio is reached, and means resetting all divider sections to reference conditions for succedent counting upon the production of each output signal.

2. A frequency divider operative to produce division of an applied signal by selectable whole number ratios comprising, a plurality of divider sections connected in cascade, one for each decimal digit of the selected division ratio, counter means within each section registering in combinations of conductivity conditions therein, the quantity of input signals, primary reset signal means for each counter resetting the counter to a reference condition following each registry of a number of signals equal to the value of the corresponding decimal digit, secondary reset si nal means for each counter resetting the counter to the reference condition following each subsequent registry of ten signals, an output signal path providing an output signal of frequency reduced from the input upon registry of the desired count in the highest order digit of the selected division ratio, and means responsive to the production of each output signal to reset all sections to a reference condition.

3. A frequency divider responsive to produce division of applied signals comprising, a counter capable of registering at least ten counts for an equal number of applied signals, primary selector means responsive to counter registry to produce primary output signals the first time a selected count less than ten is registered, means blocking the primary selector means following the produc tion of a primary signal, secondary selector means responsive to counter registry to produce secondary output signals for each tenth succeeding input signal, and means unblocking the primary selector means after the production of a selected quantity of secondary output signals.

4. A frequency divider responsive to produce division of applied electrical signals comprising, a binary electrical counter capable of registering at least ten characteristic combinations of binary conditions responsive to ten applied signals, a primary selector adjustable to provide a primary output signal upon the attainment of a binary combination characteristic of applied signals in quantity between one and nine, means blocking the primary selector means after the production of each primary output signal, a secondary selector fixed to provide secondary output signals upon the attainment of the binary combination characteristic of ten applied signals, means resetting the counter to the reference condition following each primary and secondary output signal, and means unblocking the primary selector after the production of a selected quantity of secondary output signals.

5. In combination, a first frequency divider section comprising four scale-of-two counter stages connected in cascade possessing sixteen possible states of conduction including a zero state, a reset circuit connected to said stages to return the same to the zero state upon the receipt of an impulse, a control circuit connected to said counter stages selectively responsive to any state between one and nine to produce an impulse, a signal path feeding the initial impulse from said control circuit to said reset circuit and thereafter insensitive to subsequent impulses, a second control circuit connected between said counter stages and reset circuit to furnish said reset circuit with an impulse responsive to the attainment of the tenth state of said counter stages, a second similar divider circuit connected to receive as input signals the impulses from said second control circuit, additional divider sections similarly connected in cascade with one another, and means responsive to the output from the final section for actuating all reset circuits and simultaneously enabling said signal paths.

6. In combination, a first frequency divider section comprising four scale-of-two counter stages connected in cascade possessing sixteen possible states of conduction including a zero state, a reset circuit connected to said stages to return the same to the zero state upon the receipt of an impulse, a control circuit connected to said counter stages selectively responsive to any state be tween one and nine to produce an impulse, a signal path feeding the initial impulse from said control circuit to said reset circuit and thereafter insensitive to subsequent impulses, a second control circuit connected between said counter stages and reset circuit to furnish said reset circuit with an impulse responsive to the attainment of the tenth state of said counter stages, and means fed from the output of the second control circuit for enabling said signal path in response to the production of a selected number of output signals from said second control circuit and thereby simultaneously actuating said reset circuit.

GAROLD K. JENSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,087,039 McMaster July 13, 1937 2,295,968 Poole Sept. 15, 1942 2,401,729 Goldsmith June 11, 1946 2,422,698 Miller June 24, 1947 2,490,500 Young Dec. 6, 1949 OTHER REFERENCES Predetermined Counter, J. J. Wild, Electronics, March 1947, pages -123.

Predetermined Counters, R. J. Blume, Electronics, February 1948, pages 88-93. 

